1. Field of the Invention
The present invention relates to an injection control method and an injection control unit for a die-casting machine, more particularly, which can be used for injection control of a die-casting machine in which an injection velocity is controlled to turn out high-quality die cast products.
2. Description of Related Art
It has so far been known that the quality of a die cast product is greatly influenced by an injection velocity and an injection pressure when melt is charged into a mold. Therefore, various considerations are given to the control of these velocity and pressure.
For example, in injecting melt into the mold by using an injection cylinder unit, a procedure is used in which an injection plunger is first advanced at a low velocity so as to prevent melt in a passage from bubbling, and when the front end of melt reaches the interior of the mold, the advance velocity is switched to a high velocity to charge the melt into the mold by pushing it at a stroke.
These injection operations must be performed exactly during a short period of time before the melt solidifies. Therefore, if control of various operational conditions is carried out manually, a satisfactory result cannot be obtained, and also the work efficiency is decreased. These setting operations are performed rapidly by a skilled worker, but it is desired that they be performed properly by everybody.
In view of the above-described situation, there has been developed a technology for automatically controlling a series of injection operations ranging from low-velocity injection to high-velocity injection for a die-casting machine.
For example, in the control method for a die-casting machine proposed by the applicant of the present invention (Unexamined Japanese Patent Publication No. 9-253824), the target values of a low injection velocity and a high injection velocity are set in advance, and a value (mean value thereof) detected in the actual injection operation is compared with the target values. By correcting control values so as to eliminate the difference, control can be accomplished so that the actual injection state automatically approaches the target state.
In the above-described control method for a die-casting machine, although a high-velocity injection operation and a low-velocity injection operation are controlled, it is difficult to carry out control over the whole section of injection operation.
Also, since there is gate resistance depending on mold characteristics, it is not easy to issue a velocity command to be executed by open loop control of injection velocity from the beginning.
Besides, since the die-casting machine used mainly at present is based on position feedback, it is required to ensure affinity with the position feedback system.